The invention relates to a device for determining the quality of an output signal to be generated by a signal processing circuit with respect to a reference signal, which device is provided with a first series circuit having a first input for receiving the output signal and is provided with a second series circuit having a second input for receiving the reference signal and is provided with a combining circuit, coupled to a first output of the first series circuit and to a second output of the second series circuit, for generating a quality signal, which first series circuit is provided with
a first signal processing arrangement, coupled to the first input of the first series circuit, for generating a first signal parameter as a function of time and frequency, and PA1 a first compressing arrangement, coupled to the first signal processing arrangement, for compressing a first signal parameter and for generating a first compressed signal parameter, which second series circuit is provided with PA1 a second compressing arrangement, coupled to the second input, for generating a second compressed signal parameter, which combining circuit is provided with PA1 a differential arrangement, coupled to the two compressing arrangements, for determining a differential signal on the basis of the compressed signal parameters, and PA1 an integrating arrangement, coupled to the differential arrangement, for generating the quality signal by integrating the differential signal with respect to time and frequency. PA1 a further integrating arrangement for integrating a first series circuit signal and a second series circuit signal with respect to frequency so as to generate two integrated series circuit signals, and PA1 a comparing arrangement, coupled to the further integrating arrangement, for comparing the two integrated series circuit signals and for scaling at least one series circuit signal in response to the comparison. PA1 a second signal processing arrangement, coupled to the second input, for generating a second signal parameter as a function of both time and frequency, the second compressing arrangement being coupled to the second signal processing arrangement in order to compress the second signal parameter. PA1 a multiplying, arrangement for multiplying in the time domain, a signal to be fed to an input of the signal processing arrangement, by a window function, and PA1 a transforming arrangement, coupled to the multiplying arrangement, for transforming a signal originating from the multiplying arrangement to the frequency domain, which transforming arrangement generates, after determining an absolute value, a signal parameter as a function of time and frequency. PA1 a subband filtering arrangement for filtering a signal to be fed to an input of the signal processing arrangement, which subband filtering arrangement generates, after determining an absolute value, a signal parameter as a function of time and frequency. PA1 a converting arrangement for converting a signal parameter represented by means of a time spectrum and a frequency spectrum to a signal parameter represented by means of a time spectrum and a Bark spectrum. PA1 generating a first signal parameter as a function of time and frequency in response to the output signal, PA1 compressing a first signal parameter and generating a first compressed signal parameter, PA1 generating a second compressed signal parameter in response to the reference signal, PA1 determining a differential signal on the basis of the compressed signal parameters, and PA1 generating a quality signal by integrating the differential signal with respect to time and frequency. PA1 reducing the amplitude of the differential signal. PA1 reducing the amplitude of the differential signal in dependence of at least either a first signal to be generated in response to the output signal or a second signal to be generated in response to the reference signal. PA1 integrating, with respect to frequency, a further first signal to be generated in response to the output signal and a further second signal to be generated in response to the reference signal, PA1 comparing the integrated further first signal and the integrated further second signal, and PA1 scaling at least one of the further first signal and the further second signal in response to the comparison. PA1 generating a second signal parameter in response to the reference signal as a function of both time and frequency, and PA1 compressing a second signal parameter. PA1 multiplying in the time domain a still further first signal to be generated in response to the output signal by a window function, and PA1 transforming the still further first signal to be multiplied by the window function to the frequency domain, which represents, after determining an absolute value, a signal parameter as a function of time and frequency. PA1 filtering a still further first signal to be generated in response to the output signal, which represents, after determining an absolute value, a signal parameter as a function of time and frequency. PA1 converting a signal parameter represented by means of a time spectrum and a frequency spectrum to a signal parameter represented by means of a time spectrum and a Bark spectrum.
Such a device is disclosed in the first reference: J. Audio Eng. Soc., Vol. 40, No. 12, Dec. 1992, in particular "A Perceptual Audio Quality Measure Based on a Psychoacoustic Sound Representation" by John G. Beerends and Jan A. Stemerdink, pages 963-978, more particularly FIG. 7. The device described therein determines the quality of an output signal to be generated by a signal processing circuit, such as, for example, a coder/decoder, or codec, with respect to a reference signal. The reference signal is, for example, an input signal to be presented to the signal processing circuit, although the possibilities also include using, as the reference signal, a pre-calculated ideal version of the output signal. The first signal parameter is generated as a function of time and frequency by means of the first signal processing arrangement, associated with the first series circuit, in response to the output signal, after which the first signal parameter is compressed by means of the first compressing arrangement associated with the first series circuit. In this connection, intermediate operational processing of the first signal parameter should not be ruled out at all. The second signal parameter is compressed by means of the second compressing arrangement, associated with the second series circuit, in response to the reference signal. In this case too, further operational processing of the second signal parameter should not be ruled out at all. Of both compressed signal parameters, the differential signal is determined by means of the differential arrangement associated with the combining circuit, after which the quality signal is generated by integrating the differential signal with respect to time and frequency by means of the integrating arrangement associated with the combining circuit.
Such a device has, inter alia, the disadvantage that the objective quality signal, to be assessed by means of the device, and a subjective quality signal, to be assessed by human observers, have a poor correlation with each other.